Damascene reticle and method of manufacture thereof

ABSTRACT

A method for manufacturing an optical projection reticle employs a damascene process. First feature recesses are etched into a projection reticle mask plate which is transmissive or transparent. Then feature recesses are tilled with a radiation transmissivity modifying material comprising a partially transmissive material and/or a radiation absorber for absorbing actinic radiation. Sacrificial materials may be added to the recess temporarily prior to filling the recess to provide gaps juxtaposed with the material filling the recess. Thereafter, the sacrificial materials are removed. Then the projection mask is planarized leaving feature recesses filled with transmissivity modifying material, and any gaps desired. The projection mask is planarized while retained in a fixture holding it in place during polishing with a polishing tool and a slurry.

BACKGROUND OF THE INVENTION

The present invention relates to methods of manufacture ofphotolithographic reticles, i.e. masks, and reticles produced thereby.More particularly this invention relates to methods for fabrication ofreticles for exposure of microelectronic integrated circuits and othermicro-scale devices and to the reticles produced thereby.

During the process of manufacturing of microelectronic integratedcircuits on a substrate comprising a workpiece such as a semiconductorwafer or the like, layers of material on the workpiece are patternedphotolithographically. A layer of a radiation sensitive resist(hereinafter resist) is deposited on the workpiece. The resist (e.g.photoresist) comprises a radiation sensitive material which can beexposed to a master image projected as patterns of radiation, e.g.light, ultraviolet light, x-ray, electron beam, or other forms ofradiation. The resist is later exposed using an exposure tool, and areticle. The reticle comprises a photomask or the like which ispatterned with opaque regions, transparent regions and possiblypartially transparent regions. During the exposure process, radiation isdirected onto the reticle to expose the resist selectively with patternsof radiation projected through the reticle.

The resist is developed, and then the remaining resist forms a mask onthe workpiece which protects areas of the workpiece during subsequentfabrication processes, such as deposition, etching, or ion implantation.A mask or photomask is generally used for photoimaging with a positiveor negative image when exposing a photosensitive material known asphotoresist or analogous materials sensitive to electromagnetic or otherforms of radiation.

Binary Reticle

A binary reticle includes a pattern corresponding to features to beformed on work pieces such as FET devices or other Integrated Circuit(IC) features. A binary reticle may be formed on a reticle mask platecomprising a transparent glass plate coated with a patterned, opaque(light blocking) material. This type of reticle is typically referred toas a binary mask since some of the Sight is completely blocked by theopaque material and the remainder of the light is fully transmittedthrough the transparent, glass portions.

Chrome On Glass (COG) Binary Reticle

A Chrome-On-Glass (COG) reticle (i.e. a mask, photomask, orphotoreticle) typically comprises a quartz-chrome patterned mask. Inmore detail, a COG reticle comprises a single crystal quartz reticlemask plate that is substantially planar, which carries a mask patterndefined using a patterned chrome (Cr/CrO₂) layer, formed by sputtering.The chrome layer is laminated to the top surface of the reticle maskplate. A virgin or blank COG reticle mask plate or mask blank comprisesa virgin reticle which has not been patterned. In other words, a virginCOG reticle comprises an unpatterned or blank planar layer of chromedeposited on a quartz reticle mask plate.

In the production of a COG patterned reticle, e.g. an Integrated CircuitDevice (ICD), an image of one or more microelectronic devices is printedonto a virgin COG reticle via a lithographic process by exposure toradiation. A layer of resist is applied to the blank COG reticle maskplate covering the top surface of the chrome layer. After patterning byexposure of the resist to a master image, the resist is developed toreproduce the exposed pattern thereby producing openings down to thesurface of the chrome of the COG mask. Exposed surfaces of the COG maskare removed by etching leaving the remaining portions of the chromelayer intact. Then the resist is removed with appropriate chemicals andwashed away.

In the context of photolithography, the term reticle refers to asemiconductor photomask, which contains an image which is adapted toexpose only a small part of a semiconductor wafer which is to beemployed in a step-and-repeat exposure system, i.e. a wafer stepper orscanner. A semiconductor reticle typically contains the pattern of aseveral semiconductor devices. The reticle is employed in the waferstepper to project an image to be exposed over and over onto a workpiececomprising a semiconductor wafer covered with unexposed photoresist bymoving the workpiece relative to the reticle with the wafer stepper orscanner, which is employed to expose several areas of the unexposedphotoresist repeatedly and sequentially.

In addition to visible light, the absorber may be capable of absorbingration such as infra-red, x-ray, E-beam, or light in ranges such as theUltra Violet (UV) range, Deep Ultraviolet (DUV) range, VacuumUltraviolet (VUV) range, and Extreme Ultra Violet range (EUV).

The present invention relates to processing of integrated circuitdevices and particularly to the manufacturing of optical projectionmasks for deep submicron (<0.25 μm) integrated circuit processes.

A common method of manufacturing of projection reticles for exposure ofintegrated circuit devices has relied on etching a pattern into anactinic radiation absorber comprising a layer of absorbent materialwhich is deposited on a reticle mask plate (i.e. a transparent substrateor mask blank.) Currently in semiconductor fabrication the patterning ofstructures on a substrate is often performed with reticles defined bylithography performed on a blank COG reticle.

There is a serious problem with the process of etching through thechrome of a COG reticle mask plate down to the quartz therebelow whichis that the etching process for the chrome also consumes the photoresistmask very quickly which forces certain restrictions in the mask makingprocess (e.g. resist thickness.)

There are other serious problems with etched COG reticles. One suchproblem with etched COG reticles is that Electro-Static Discharge (ESD)can cause damage to the metal (chrome) pattern on a substrate composedof quartz as the insulating material. The problem is that unwantedElectro-Static Discharge (ESD), involving rapid dissipation of electriccharge in a short amount of time, often causes delamination of thechrome pattern from the quartz substrate. In other words, at least aportion of the chrome pattern on the quartz substrate is lifted awayfrom the top surface thereof, as the ESD energy is being dissipated inthe laminated material. That renders the mask defective so that it isnot useful for the fabrication of devices on semiconductor substrates.

Another serious problem with COG reticles is that they grow defects overthe lifetime of the mask which limits the useful lifetime of suchreticles and forces regular cleaning.

Phase Shift Mask (PSM)

Another type of reticle is the Phase Shift Mask (PSM), which can beproduced by allowing some light to pass through a partially-transmissivechrome feature thereby changing the phase of the light that passestherethrough, i.e. creating phase shifted light. The phase shifted lightfrom the partially-transmissive feature affects the interference patternof the light transmitted from neighboring fully transparent areas,resulting in a higher contrast at the imaging plane. This allows imagingfeatures with significantly smaller feature sizes than would be possibleusing the same mask pattern implemented as a standard COG reticle. Thesereticles are referred to as attenuated PSM (AttPSM) reticles.

Alternating PSM (AltPSM) Mask

A third type of reticle is known as an Alternating PSM (AltPSM) reticle(mask) wherein feature recesses are etched into the virgin reticle maskplate. The feature recesses result in a path length difference for thelight passing therethrough, and the depth of the feature recess is tunedto result in a 180° phase shift of the incident electromagneticradiation to be used in exposure of the image on the reticle. The AltPSMmask has limitations in that the termination of features can bedifficult and a second mask called a block out has to be used inconjunction therewith to terminate the features that are desired on thesubstrate. The higher cost of these AltPSM reticle processes isnegligible in view of expenses saved as compared to more advancedlithography tooling that would be required when only COG reticles wouldbe used. However the cost of fabrication of a mask set has increaseddramatically by introducing those extra processing steps required forAltPSM reticle processing.

Commonly assigned U.S. Pat. No, 5,932,377 of Ferguson et al, entitled“Exact Transmission Balanced Alternating Phase-Shifting Mask forPhotolithography” describes forming an AltPSM mask with etched-quartztrenches. It states that a phase difference between two clear shapes foran AltPSM is achieved in standard industry practice by selectivelyetching into a quartz reticle mask plate so an optical path differenceequivalent to the desired phase offset is obtained between two adjacentopenings. After standard mask patterning, a second write step is used toselectively open a protective resist coating for a phase-shifted openingleaving a non-phase shifted opening covered. Typically, the quartz isthen etched with an anisotropic Reactive-Ion Etching (RIE) process.

Commonly assigned U.S. Pat. No. 5,565,286 of Lin entitled “CombinedAttenuated-Alternating Phase Shifting Mask Structure and FabricationMethods Therefor” describes a structure and fabrication method for aphase-shifting lithographic mask. Att PSM and AltPSM are combined toprovide a mask combination consisting of phase-shifted and unshiftedattenuated backgrounds in which the phase-shifted attenuated backgroundsurrounds the unshifted components and the unshifted attenuatedbackground surrounds the phase-shifted components.

U.S. Pat. No. 6,660,653 of Tzu et al. entitled “Dual Trench AlternatingPhase Shift Mask Fabrication” describes fabricating a dual-trench AltPSMmask. A chromium layer formed over a quartz layer of the PSM ispatterned with deep trenches by dry etching through a photoresist layer.The quartz layer is dry etched through another photoresist layer appliedover the chromium layer and patterned according to the deep trenches andthe shallow trenches of the AltPSM design using backside exposure toultraviolet light.

Damascene Patterning

Traditionally, the term damask refers to rich tapestry patterns ofdamask silk, such as a figured fabric of silk, wool, linen, cotton, orsynthetic fibers, with a pattern formed by weaving. An artisticdamascene process of metal work involves inlaying metal into trenches inanother metal is a process of inlaying different metals into oneanother, e.g. gold or silver into a darkly oxidized steel background, toproduce intricate patterns.

In semiconductor technology, damascene or dual-damascene metalpatterning processes have been employed in forming copper interconnectsin a dielectric layer, e.g. silicon oxide, for external electricalconnections and interconnections of semiconductor devices. Thesemiconductor damascene process starts by a subtractive process ofetching open trenches reaching down into a dielectric layer whereincopper conductor patterns are to be formed. An additive patterningprocess is employed involving deposition of a conformal barrier layerfollowed by deposition of a blanket (thick) coating of copper thatsignificantly overfills the trenches. Then, the excess copper is removedby planarization to the level of the top of the insulating layer byChemical-Mechanical Polishing (CMP). The copper, which remains withinthe trenches of the insulating layer, comprises a patterned interconnectconductor.

U.S. Pat. No. 6,821,192 of Donohue entitled “Retaining Ring for Use inChemical Mechanical Polishing” describes a retaining ring for use on acarrier head in a Semiconductor Wafer CMP (SWCMP) apparatus with abottom surface, an inner surface and an outer surface, and a pluralityof recesses on the bottom surface. Each recess includes an innertrailing surface and a slurry capture area. A channel connects theslurry capture area to the inner surface. The inner trailing surface canbe configured for fastening thereon an insert tool having a contact edgefor abrasively contacting a polishing pad. The Donohue patent states“Integrated circuits are typically formed on substrates, particularlysilicon wafers, by the sequential deposition of conductive,semiconductive or insulative layers. After each layer is deposited, thelayer is etched to create circuitry features. As a series of layers aresequentially deposited and etched, the outer or uppermost surface of thesubstrate, i.e., the exposed surface of the substrate, becomessuccessively less planar. This non-planar outer surface presents aproblem for the integrated circuit manufacturer as a non-planar surfacecan prevent proper focusing of the photolithography apparatus.Therefore, there is a need to periodically planarize the substratesurface to provide a planar surface. Planarization, in effect, polishesaway a non-planar, outer surface, whether a conductive, semiconductive,or insulative layer, to form a relatively flat, smooth surface.”

Transmissivity, τ and Opacity

Transmissivity in the context of this invention is defined as thetraction of incident radiation (at actinic wavelength) that passesthrough a mask, more specifically, a mask plate or combination ofmaterials in or on the mask plate. In the context of this invention amaterial is considered to be transparent if it has a maximum value oftransmissivity equal to that of the mask plate or substrate without anyother materials than quartz. Opacity is defined as the fraction ofincident radiation (at actinic wavelength) that is absorbed whilepassing through a mask, more specifically, a mask plate or combinationof materials in or on the mask plate. In the context of this invention amaterial is considered to be opaque (having a value of opacity nearing avalue of 1) if practically all the light is absorbed in the material,e.g. darkly pigmented glass.

An object of this invention is to avoid the difficult absorber etchemployed in the subtractive process employed in patterning COG masks.

Another object of this invention is to provide a method for fabricatingan optical projection mask using DUV resists.

Still other objects of this invention are maximizing the choices ofabsorbing materials for the optical projection mask manufacturer; toincrease throughput on pattern generating tools in the mask makingenvironment (higher sensitivity of DUV resists); minimizing scatteringfrom the projected pattern by adding a liner to function as a lens;focusing the exposure rays at the edge of the pattern to increase signalto noise levels; and using of different absorbing materials, thereforeallowing to tune linewidth per exposure.

A further object of this invention is to provide a reticle carrier tohold the reticle during polishing with the carrier consisting of a metalbase plate that, has a number of passages through it; and to provide areticle holding ring that is made of a low friction material thatattaches to the base plate.

SUMMARY OF THE INVENTION

The present invention utilizes techniques that will allow the formationof a reticle by creating structures in a virgin reticle mask plate, theformation of which structures presents an opportunity to create multiplefeatures that are not presently available in mask processing today.

This invention leaves the top surface of a reticle which is completelyplanar, improving the imaging performance by reducing the scattering oflight between features. Such a fully planar surface also allows thesealing of the top surface of the reticle without adverse effects,eliminating growth of defects on the features of the reticle.

One aspect of this invention allows the difficult process of absorberetching to be replaced by a silicon dioxide etch into the quartz of aCOG plate to form an etched pattern, followed by the process of fillingthe etched pattern with an actinic absorber.

As employed herein the term reticle is intended to be interpreted to besynonym of the terms mask, photomask, and photoreticle.

In accordance with this invention, a damascene method for manufacturingoptical projection masks comprises patterning a substrate for an opticalprojection mask having a first level of transmissivity with a featurerecess; and filling said recess with a material having a different levelof transmissivity.

Preferably, the method involves forming a projection reticle in atransparent substrate having a top surface with a feature recess in thetop surface of the transparent substrate; and forming a radiationtransmissivity modifying material in the feature recess. The radiationtransmissivity modifying material comprises a material selected from thegroup consisting of an opaque material and a partially transmissivematerial.

Preferably, the method involves forming a projection reticle in atransparent substrate having a top surface with a feature recess in thetop surface of the transparent substrate, and forming a radiationtransmissivity modifying material in the feature recess. The radiationtransmissivity modifying material comprises a material selected from thegroup consisting of an opaque material and a partially transmissivematerial. A plurality of films may be included in the feature recesswith the deposited films having different degrees of transmissivity.Preferably, the radiation transmissivity modifying material is selectedfrom the group comprising at least two deposited films including anopaque film and a transmissive film and an opaque film deposited with apartially transmissive material.

Preferably a liner is formed juxtaposed with the radiationtransmissivity modifying material as a lens for focusing the exposurerays at the edge of the pattern to increase signal to noise levels sothat scattering from the projected pattern is minimized. Preferably forma sacrificial material is present in the recess. Next, a material formodifying radiation transmissivity is formed juxtaposed with thesacrificial material. Then the sacrificial material is removed from therecess.

Preferably, the radiation transmissivity modifying material is depositedas a film upon the transparent substrate; and the radiation,transmissivity modifying material is planarized with a polishing slurryconsisting of fumed silica, a pH of from about 2.2 to about 2.6, and a1:10 dilution in water of on the order of one part of about 84% to about88% parts phosphoric acid to 9 parts water, preferably deionized water.

Preferably a reticle carrier is provided for a polishing tool capable ofaccommodating a reticle comprising a rigid base plate; a retaining ring;a reticle pad adapted for supporting a reticle inserted onto the reticlecarrier; and the base plate with the reticle pad having a plurality ofaligned passageways therethrough for exhaustion of air from the spacebetween the base plate and a reticle; whereby a vacuum is generated toretain a reticle in place under vacuum conditions and application of airunder pressure can eject a reticle from the reticle carrier.

It is preferred that a metal base plate is provided having a pluralityof passageways therethrough, preferably including a reticle padinstalled on the metal base plate with matching aligned plurality ofpassageways therethrough. It is also preferred that a reticle holdingring is provided made of a low friction material that is attachable tothe base plate.

In accordance with another aspect of this invention, a projectionreticle is formed in a transparent substrate having a top surfacecomprising a feature recess in the top surface of the transparentsubstrate; and a radiation transmissivity modifying material is formedin the feature recess.

Preferably, the radiation transmissivity modifying material comprises amaterial selected from the group consisting of an opaque material, and apartially transmissive material. A plurality of deposited films may beincluded in the feature recess with the deposited films having differentdegrees of transmissivity.

Preferably, the radiation transmissivity modifying material is selectedfrom the group comprising at least two deposited films including anopaque film and a transmissive film, and an opaque film deposited with apartially transmissive material.

Preferably, the radiation transmissivity modifying material comprises anopaque film juxtaposed with a phase emir correction material selectedfrom the group consisting of a solid or a gas. Preferably the recess hassidewalls and the radiation transmissivity modifying material is spacedaway from the sidewalls by the phase error correction material.

Preferably, a liner is juxtaposed with the radiation transmissivitymodifying material as a lens for focusing the exposure rays at the edgeof the pattern to increase signal to noise levels, whereby scatteringfrom the projected pattern is minimized.

In accordance with another aspect of this invention, a shiny for reticlepolishing comprises fumed silica with a pH of from about 2.2 to about2.6; and with on the order of a dilution of one part of 84-88%phosphoric acid in about 9 parts of water, preferably deionized water.

The invention and objects and features thereof will be more readilyapparent from the following detailed description and appended claimswhen taken with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1G are schematic, elevational sections of a reticle mask plateduring the process of manufacture of a damascene reticle in accordancewith this invention.

FIG. 2A shows a flow chart which describes the steps in accordance withthe process flow illustrated by the drawings from FIG. 1A to FIG. 1G;and FIG. 2B shows a flow chart which describes alternative steps inaccordance with the process flow illustrated by the drawings from FIG.1A to FIG. 1G.

FIGS. 3A-3F are schematic, elevational sections of a reticle mask plateduring the process of manufacture of another form of damascene reticlein accordance with the method of this invention in accordance with themethod of this invention.

FIG. 4 is a flow chart which describes the steps in accordance with theprocess flow illustrated by the drawings from FIG. 3A to FIG. 3F.

FIG. 5 is a perspective view depicting a reticle in accordance with thisinvention in which an annular, via type via feature is formed for astructure, e.g. a semiconductor via, in a transparent reticle maskplate.

FIG. 6 shows a perspective view depicting a reticle in accordance withthis invention in which an rectangular type line patterning feature isshown in a transparent reticle mask plate with the light passingmaterial and the light blocking material formed in a linear featurerecess leaving a narrow feature recess inside the light blocking film.

FIGS. 7A-7F illustrate an alternative process of manufacture whichprovides a patterned damascene reticle in accordance with the method ofthis invention.

FIG. 8 is a flow chart which describes the steps of the process flowillustrated by the drawings from FIG. 7A to FIG. 7F.

FIGS. 9A-9I illustrate the steps of a method of manufacture of a reticlemask plate which is patterned with feature recesses in accordance withthis invention.

In combination, FIG. 10A and FIG. 10B show a flow chart of the steps ofthe process flow illustrated by the drawings from FIG. 9A to FIG. 9I.

FIG. 11 is a perspective view depicting a reticle with an openperipheral space via feature in accordance with this invention in whichan annular, via type via feature is formed for a structure, e.g. asemiconductor via, in a transparent reticle mask plate.

FIG. 12 is a perspective view of an open peripheral space line featurein accordance with this invention depicting a reticle showing arectangular type line patterning feature in a transparent reticle maskplate with the planarized light blocking material formed in a linearfeature recess leaving a narrow feature recess inside the light blockingfilm.

FIGS. 13A and 13B show sectional and bottom views respectively of areticle polishing carrier in accordance with this invention which isadapted for use with a wafer polishing tool for the purpose of reticlepolishing.

FIGS. 14A and 14B show sectional and bottom views respectively of thereticle polishing carrier of FIGS. 13A and 13B with a reticle insertedtherein for polishing.

FIG. 15 is a table showing representative slurry formulation. FIG. 16 isa table showing the processing parameters and equipment employed forperforming an exemplary Damascene Reticle CMP (DRCMP) process inaccordance with this invention. FIG. 17 is a table showing animplementation of the DRCMP process of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The invention has a number of different embodiments. A common feature ofthe various embodiments is the use of the Damascene Reticle CMP (DRCMP)in the formation of a damascene reticle. Another feature common to allof the different embodiments is the formation of recessed trenches in atransparent plate.

Damascene Quartz Binary Reticle

In this embodiment, a damascene reticle in accordance with the inventionis formed employing photolithography. Structures are formed in and/orupon a reticle starting with a blank, planar, transparent reticle maskplate adapted for creating features in a use in processes in themanufacture of microelectronic devices.

First Embodiment of a Damascene Mask Plate Formed in a TransparentReticle Mask Plate

Heretofore, mask plate reticles have been formed by patterning opaquematerial on the top surface of a transparent substrate. In accordancewith this invention a damascene mask plate is formed by first forming apattern of recesses in a blank, transparent, reticle mask plate. Thenthe recesses are filled with opaque and/or partially transmissivematerials depending upon which type of damascene mask plate is beingformed in accordance with this invention. Several embodiments thereofare described below with reference to the appended drawings. Thesubstrate can be selected to be transparent for an exposure radiation ofan appropriate wavelength to be used with such mask plate reticles.FIGS. 1A-1F are schematic, elevational sections of a reticle 10 formedfrom a blank transparent reticle mask plate 11 (hereinafter mask plate11). The process of manufacture provides a patterned damascene reticle10 shown in FIG. 1G formed in accordance with the method of thisinvention. FIG. 2 is a flow chart which describes the steps of theprocess flow illustrated by FIGS. 1A to 1G. FIG. 1G shows a complete,patterned damascene reticle 10 in accordance with this invention aftercompletion of the manufacture thereof. The damascene reticle 10 (mask)of FIG. 1G is adapted to be employed to expose patterns formed thereon.

FIG. 1A shows the blank reticle 10 in the form of a blank, planar,transparent, reticle mask plate 11, hereinafter mask plate 11, (composedof quartz or silicon dioxide) in the initial stage of processing of stepA in FIGS. 2A and 2B with a photoresist mask PR formed thereon. The maskplate 11 has a top surface upon which a blanket layer of photoresist PRis deposited and patterned into a mask PR. The mask PR is formed inaccordance with photolithographic techniques, well understood by thoseskilled in the art. There is an open window W reaching down through themask PR exposing the top surface of the reticle mask plate 11, as willalso be well understood by those skilled in the art. The mask plate 11may comprise a virgin, planar quartz plate with no layer of chromeformed thereon. The top surface of the mask plate 11 is substantiallyflat or planar. Preferably, the photoresist mask PR may comprise astandard state-of-the-art DUV resist.

FIG. 1B shows the previously blank reticle 10 of FIG. 1A after initialpatterning by etching through the window W down into the blank maskplate 11 to form an initial feature recess 12 in the form of a trenchformed in the mask plate 11 according to step B in FIGS. 2A/2B. Theinitial feature recess 12 extends down partially through the mask plate11 from the top surface of reticle mask 10. The initial feature recess12 can be formed in a quartz or silicon dioxide mask plate 11 by using aconventional etching process, using either a wet etching or a dryetching process. For quartz or glass (silicon oxide) a wet etch can beperformed with an acidic etchant, e.g. an aqueous hydrofluoric acid (HP)solution. A dry etch can be performed by Reactive Ion Etching (RIE) witha dry etchant such as CF₄. TetraMethylAmmonium Hydroxide (TMAH) which isabase can etch the initial feature recess 12 into a silicon mask plate11. TMAH is a quaternary ammonium salt with the molecular formula(CH₃)NOH used as an anisotropic etchant of silicon; and TMAH can be usedas a basic solvent in the development of an acidic photoresist inphotolithographic processing of a workpiece.

FIG. 1C shows the reticle 10 of FIG. 1B after the photoresist mask PR isremoved from the top of the patterned, mask plate 11 in accordance withstep C in FIG. 2.

FIG. 1D shows the reticle 10 of FIG. 1C after deposition of a radiationtransmissivity modifying material on the top surface of the etched maskplate 11. In this case the radiation transmissivity modifying materialcomprises a conformal, opaque-absorber film 15C composed of an opaquematerial with a relatively uniform thickness. The absorber film 15C isdeposited on the top surface of the mask plate 11 and the side wall andbottom surfaces of the initial feature recess 12 in accordance with stepD in FIG. 2. The conformal, opaque-absorber film 15C leaves a recess 15Rdefining a shallower and narrower feature recess 12′ (representing alatent feature 15F.) The absorber film 15C preferably comprises anopaque material selected to have optical characteristics adapted toblock the radiation (e.g. light) which can be employed for exposure(onto workpieces being manufactured) of patterns of damascene featuresto be formed in the mask plate 11. One such damascene feature 15F isshown after completion of processing thereof as shown by FIG. 1G.

FIG. 1D shows how a mask plate 11 is being prepared to be patterned withthe feature 15F of FIG. 1E. Alter step D is completed the initialfeature recess 12 is narrowed (forming a potential, damascene feature15R) by the thickness of the conformal, absorber film 15C which linesthe sidewall surfaces as well as the bottom surface of the initialfeature recess 12 of FIG. 1B. In other words a narrowed feature recess12′ remains inside the initial feature recess 12. It is preferred toemploy Chemical Vapor Deposition (CVD) to deposit the absorber film 15Cwhen it comprises TaN, Ta, Ti, TiN, Ni, W, SiO₂, SiN, or SiC or acombination thereof. Other deposition techniques can also be employed todeposit film 15C, e.g. plating, atomic layer deposition, sputtering,evaporation, etc. that are all well known in the industry.

FIG. 1E shows reticle 10 of FIG. 1D after planarization by a processsuch as DRCMP in step E of FIGS. 2A/2B to remove the uppermost (outer),exposed portions of the conformal layer of opaque material 15C from thetop surface of the mask plate 11. The inner, remainder of the conformallayer of opaque material 15P is formed into a patterned, opaque,damascene feature 15F which remains on the sidewall surfaces and thebottom surface of the initial feature recess 12 of FIG. 1E leaving ashallower feature recess 12″.

FIG. 1F shows the reticle 10 of FIG. 1E after a deposition in accordancewith step F in FIG. 2A of a blanket transparent coating 16B that willallow mask exposure, radiation, i.e. light, to pass through it andthrough the mask plate 11 as well, aside from the patterned, opaque,damascene feature 15F. The transparent coating 16B covers the topsurface of the mask plate 11 and fills the shallower feature recess 12″leaving the surface of the transparent coating 16B with a depression 16Dtherein above the shallower feature recess 12″ of FIG. 1E. It ispreferred to deposit the transparent coating 16B by a CVD process.Alternatively, one can sputter and spin-on materials which are used asinsulators (i.e. SiLK from Dow Chemical and flowable oxides) which canbe deposited to form the transparent coating 168. These spin-onmaterials are applied in the same manner as photoresist. Additionally,if a spin-on component, is used, it can be planarized. The planarizingcharacteristics are dependant upon the viscosity of the material, as iswell known by those skilled in the art.

FIG. 1G shows the completed reticle 10 of FIG. 1F alter a step ofplanarization, e.g. DRCMP planarization in accordance with step G inFIG. 2A. The DRCMP planarization of step G has transformed the blanketlayer of transparent material 16B of FIG. 1F into a thin film 16P ofFIG. 1G comprising a planar remainder of the transparent coating 16Bwith a substantially planar top surface. The planar transparent coating16P continues to fill the shallower feature recess 12″ and covers thetop surface of the reticle mask plate 11, providing protection for theremainder of the conformal layer of opaque material 15P (which forms thepatterned, opaque, damascene feature 15F) and the reticle mask plate 11.

Alternatively in FIG. 2B, steps F and G have been replaced by step F′ inwhich spin coating a deposit of a blanket, planar, transparent layer 16P(as shown in FIG. 1G) covers both the mask plate 11 and the patterned,opaque, damascene feature 15F formed from the absorber film 15C.

In the processing in accordance with FIGS. 2A and 2B, it is preferableto deposit the layers by Chemical Vapor Deposition (CVD), whereapplicable.

Second Embodiment: Damascene PSM Reticle

FIGS. 3A-3F are schematic elevational views of a damascene PSM reticle30 during the process of manufacture of the reticle in accordance withanother aspect of the method of this invention, as shown by the flowchart of FIG. 4. FIGS. 3A-3F illustrate process flow for patterning thereticle 30. As shown in FIG. 3F, the resulting reticle 30 has PSMfeatures 36F′ which are composed of deposited conformal film elements33P/35P filling a feature recess 32 in a mask plate 31. The reticle 30is adapted to be used to expose patterns on a workpiece (not shown.)FIG. 3F shows a patterned reticle 30 which is to be employed as a PSMmask after the manufacture thereof in accordance with this invention forexposing patterns formed thereon.

FIG. 3A shows the reticle 30 in an initial, stage of processing inaccordance with step A in FIG. 4. A transparent reticle mask plate 31(hereinafter mask plate 31) is shown with a top surface on which aphotoresist mask PR is formed. As with FIG. 1A, an open window W throughphotoresist mask PR reaches down to the top surface of the mask plate31, which, may comprise a virgin, planar quartz plate with no layer ofchrome formed thereon. The top surface of the mask plate 31 is flat orplanar.

FIG. 3B shows the reticle 30 of FIG. 3A after an initial feature recess32 was etched into the top surface of the mask plate 31 in accordancewith step B in FIG. 4. In step B, the reticle mask plate 31 is etchedwith a conventional etching process, as described above with referenceto step B in FIG. 2.

FIG. 3C shows the reticle 30 of FIG. 3B after removal of photoresistmask PR from the top surface of the mask plate 31 according to step C inFIG. 4.

FIG. 3D shows the reticle 30 of FIG. 3B after deposition of a radiationtransmissivity modifying material, which in accordance with step G inFIG. 4 comprises a conformal, partially-transmissive film 33C (i.e.partially-transparent film). The partially-transmissive film 33C isdeposited on the top surface of the reticle 30 and the side walls andthe bottom surface of the etched, initial, feature recess 32 leaving anarrower feature recess 32′ (forming a potential, damascene feature 33R)representing a stage in the patterning of a feature 36F′ shown in FIG.3F. The conformal, partially-transmissive film 33C is selected to haveoptical characteristics adapted to provide partial blocking of theradiation (e.g. light) that can be employed for exposure (ontoworkpieces being manufactured) of patterns of features 36F formed on thereticle 10. In FIG. 3F the feature 36F″ is shown after completion ofprocessing of the device 30 by step I in FIG. 4 of CMP planarization topolish down both the actinic absorber film 35C and thepartially-transmissive film 33C (i.e. partially-transparent film) toexpose the top surface of the mask plate 31 forming an opaque patterneddamascene feature 36F′ defined by the portions of both films remainingin the recess in the mask plate reticle 10.

Summarizing, when step G in FIG. 4 is completed the initial featurerecess 32 is narrowed into narrower feature recess 32′ and reduced indepth by the thickness of the partially-transmissive film 33C whichlines the sidewall surfaces and the bottom surface of the etched initialfeature recess 32 of FIG. 3C forming the potential, damascene feature33R. In other words a narrowed feature recess 32′ remains inside theetched initial feature recess 32 which is lined with thepartially-transmissive film 33C.

FIG. 3E shows the patterned reticle 30 of FIG. 3D after a conformal,actinic/light blocking, opaque-absorber film 35C is formed thereover inaccordance with step H in FIG. 4. Thus, both laminated films 33C/33Rincluding the partially-transmissive, conformal film 33C and theconformal, opaque-absorber film 35C cover the reticle 30. Theopaque-absorber film 35C is deposited over the patterned reticle 30 witha relatively uniform thickness on the top surface of thepartially-transmissive film 33C including the sidewall and bottomsurfaces of the feature recess 32′. As a result, the opaque-absorberfilm 35C produces a potential feature 36F in the even narrower featurerecess 32″. The conformal, opaque-absorber film 35C preferably comprisesan opaque material selected to have optical characteristics adapted toblock the radiation (e.g. light) which can be employed for exposure(onto workpieces being manufactured) of patterns of damascene featuresto be formed in the mask plate 11. One such damascene feature 36F′ isshown after completion of processing thereof as shown by FIG. 3F.

FIG. 3F shows the reticle 30 of FIG. 3E after the step I in FIG. 4 ofplanarization of the two laminated films 35C/33C down to the top surfaceof the mask plate 31. The initial feature recess 32 remains lined withthe damascene PSM feature 36F composed of the combination of a remainderelement 33P from partially-transmissive film 33C and a remainder element35P from opaque-absorber film 35C (nested in remainder element 33P)which form the resulting damascene feature 36F′. In step I of FIG. 4 theconformal, opaque-absorber, actinic or light blocking film 35C, and theconformal partially-transmissive film 33C are polished away from the topof the reticle mask plate 31 by CMP planarization forming the damascenePSM Reticle 30. Thus, the resulting feature 36F′ comprises the laminatedcombination of the remaining conformal partially-transmissive remainderfilm 33P which lines the sidewalls and bottom surface of the initialfeature recess 32 and the remaining conformal, opaque-absorber film 35Pwhich lines the conformal partially-transmissive remainder film 33P inthe feature recess 32, leaving a shallower, narrowed feature recess 32″within the opaque-absorber remainder film 35P.

The blanket films 33C/35C may be composed of a material selected fromSilicon Oxide (SiO₂), Silicon Nitride (Si₃N₄), and chromium (Cr) may bedeposited on the reticle mask plate 31. These are known materials andoffer options of not just passing light, but also changing the light.Those changes in the light can be employed to provide attenuation orphase shifting.

Third Embodiment: Damascene PSM Reticle In-Situ Lens Formation on theReticle

In a modification of the embodiment of FIG. 3F, aside from the detailthat the shape and index of refraction of the outer,partially-transmissive, remainder element 33P is tuned so that parallelfocused light beams come out of the top side of the reticle 30 asillumination is to be projected from below for all images. Improvementscan employ multiple different layers with varying refraction indexes toimprove the focus effect.

Fourth Embodiment: Via Feature

FIG. 5 is a top perspective view depicting a reticle 50 in accordancewith this invention in which an annular, via type via feature 56F isformed for a structure, e.g. a semiconductor via, in a mask plate 51.The reticle 50 is made in accordance with the method of this invention,as shown by the FIG. 4 flow chart. In this case, as in FIGS. 3B and 3Cand steps B and C in FIG. 4, a cylindrical initial feature recess 52 isformed in the reticle mask plate 51 by etching down into the mask plate51. Then the initial feature recess 52 is lined with a conformal lightpassing film 33P (deposited as in FIG. 3D, according to step G in FIG.4) which forms a narrower cylindrical recess 52′. Next the additionalnarrower cylindrical recess 52′ is lined with a conformal light blockingfilm 35P (deposited as in FIG. 3B, according to step H in FIG. 4)covering the sidewalls and bottom thereof. Then a planarization step Iin FIG. 4 is performed producing a via patterning feature 56F. A hollowwell 52W remains inside the conformal light blocking film 35P.

Fifth Embodiment: Line Feature

FIG. 6 shows a top perspective view depicting a reticle 60 in accordancewith this invention in which an rectangular type line patterning feature66F is shown in a transparent reticle mask plate 61 (hereinafter maskplate 61) with the light passing material 33P and the light blocking 35Pmaterial formed in a linear feature recess 62 leaving a narrow featurerecess 62W inside the light blocking film 35P. The reticle 60 is made inaccordance with the method of this invention, as shown by the flow chartof FIG. 4. In this case, as in FIGS. 3B and 3C, the rectangular initialfeature recess 62 is etched into the mask plate 61. Then the rectangularinitial feature recess 62 is lined with a conformal light passing film33F (deposited as in FIG. 3D, according to step G in FIG. 4) forming anarrower rectangular recess. Next the additional narrower rectangularrecess is lined with a conformal light blocking film 35P (deposited asin FIG. 3E according to step H in FIG. 4) covering the sidewalls andbottom of the additional narrower rectangular recess. Then theplanarization step I in FIG. 4 produces line patterning feature 66F.Thus the hollow well 62W remains inside the conformal light blockingfilm 35P. In summary, the line patterning feature 66F was formed in therectangular initial feature recess 62.

Sixth Embodiment: Light Blocking Material Embedded in a Reticle

FIGS. 7A-7F are schematic elevational views of the steps of forming areticle 70 from a blank, transparent, reticle mask plate 71 (hereinaftermask plate 71) illustrating an alternative method of manufacture of apatterned damascene reticle 70 in accordance with the method of thisinvention. FIG. 7F shows a complete, patterned damascene reticle 70 inaccordance with this invention after completion of the manufacturethereof. In FIG. 7F a fully opaque feature 75F is embedded in a featurerecess 72 in the mask plate 71 of the reticle 70. FIG. 8 is a flow chartwhich describes the steps of the process flow illustrated by thedrawings from FIG. 7A to FIG. 7F. The damascene reticle 70 (mask) ofFIG. 7F is adapted to be employed to expose patterns formed thereon.

In FIG. 7A, the process begins with a blank, planar, transparent reticlemask plate 71 in an initial stage of processing in accordance with stepA in FIG. 8 with a photoresist mask PR formed thereon. The mask plate 71(composed of quartz or silicon dioxide) has a top surface upon which ablanket layer of photoresist PR is deposited and then patterned into aphotoresist mask. The mask PR is formed in accordance withphotolithographic techniques which are well understood by those skilledin the art. There is an open window W reaching down through thephotoresist mask PR exposing the top surface of the mask plate 71, aswill also be well understood by those skilled in the art. Thetransparent reticle mask plate 71 may comprise a virgin, planar quartzplate with no layer of chrome formed thereon. The top surface of themask plate 71 is substantially flat or planar. Preferably, thephotoresist mask PR comprises a standard DUV resist.

FIG. 7B shows the previously blank reticle 70 of FIG. 7A after initialpatterning by etching through the window W down into the blank maskplate 71 to form a feature recess 72 in the form of a trench formed inthe mask plate 71 extending down from the top surface of the mask plate71 in accordance with step B in FIG. 8. In step B, the feature recess 72can be formed in a quartz or silicon dioxide, mask plate 71 by etchingthe feature recess employing a conventional etching process; or by usingeither a wet etching or a dry etching process as described above.

FIG. 7C shows the reticle 70 of FIG. 7B in accordance with step C inFIG. 8, after the photoresist mask PR is removed from the top surface ofthe mask plate 71 in accordance with step C in FIG. 8.

FIG. 7D shows the reticle 70 of FIG. 7C after deposition of a blanket,opaque-absorber film 75B composed of an opaque material with arelatively uniform thickness on the top surface of the mask plate 71,which fills the feature recess 72 in accordance with step J in FIG. 8,leaving a depression 7513 over the feature recess 72. The opaquematerial of the absorber film 75B, which preferably has opticalcharacteristics adapted to block the radiation (e.g. light), can beemployed for exposure (onto workpieces being manufactured) of patternsof damascene features to be formed in the mask plate 71. One suchdamascene feature 75F is shown after completion of processing thereof asshown by FIG. 7G. The layer 75B is opaque to the actinic wavelength andcompletely fills up the feature recess 72, which is a patterned trench.

FIG. 7E shows the reticle 70 of FIG. 7D after a planarization step suchas DRCMP to remove the outer, exposed portions of the blanket opaqueabsorber film 75B from the top surface of the mask plate 71 inaccordance with step K in FIG. 8. The inner, remainder 75P of theblanket, opaque absorber film 75B is formed into a patterned, opaque,damascene feature 75F remaining in the feature recess 72 of FIG. 7E.

FIG. 7F shows the completed reticle 70 of FIG. 7E after deposition inaccordance with step L in FIG. 8 of a blanket, transparent coating film77 covering the remainder 75P of the film 75B (i.e. the patterned,opaque, damascene feature 75F) and the top surface of the mask plate 71.The transparent coating film 77 allows mask exposure, radiation, i.e.light, to pass through it and through the mask plate 71 as well, asidefrom the patterned, opaque, damascene feature 75F. The transparentcoating 77 provides protection from use or handling by encapsulating theremainder of the opaque absorber film 75P (which forms the patterned,opaque, damascene feature 75F) and the mask plate 71.

Eighth Embodiment: Encapsulated Materials and Variable Index ofRefraction

FIGS. 9A-9I illustrate the steps of a method of manufacture of a reticlemask 100 patterned with feature recesses in accordance with thisinvention. FIGS. 10A/10B show a flow chart of the processing steps shownby FIGS. 9A to 9I.

In the method of FIGS. 9A-9I and the flow chart of FIGS. 10A/10B, areticle 100 is formed in a transparent reticle mask plate 101(hereinafter mask plate 101) shown in FIG. 9A. Pattern the mask plate101 with feature recesses 102 with sidewall surfaces 102S and bottomsurfaces 102B (FIGS. 9B/9C). Then deposit a conformal sacrificial film103C covering exposed surfaces on the top of the patterned mask plate101 including the exposed surfaces 102S/102B forming narrowed featurerecesses 102′ (FIG. 9D.) Next etch back the conformal sacrificial film103C is using an anisotropic inside spacer process that leaves recessedsacrificial film sidewalls 103S on the sidewalls 102S, while exposingthe bottom surfaces 102B forming deepened narrowed feature recesses 102″(FIG. 9E.)

Then deposit a conformal opaque film 105C (FIG. 9F), covering exposedsurfaces including the bottom surfaces 102B forming a pair ofpreliminary features 105R with narrower and shallower feature recesses102′″. Then in a DRCMP step, remove the external portion of theconformal opaque film 105C from the top surface of the reticle 100 (FIG.9G) forming modified features 105F with shallower recesses 102F. Next,remove the recessed portions of the sacrificial film 103S leaving gaps107O between the sidewalls 102S and the features 105F (FIG. 9H). Thegaps 107O can be filled, preferably with a gas or generation of a vacuumemploying conventional equipment as will be well understood by thoseskilled in the art. If a gas is used it is preferable to fill the gap107O with an inert gas to prevent unwanted reactions with the solidmaterials. Finally deposit a protective capping layer 109 over thefeatures 105F. At this point perform a planarizing step can be (notshown) if needed.

FIG. 9A shows the reticle 100 in an initial stage of processingaccording to step A in FIG. 10A. A blank mask plate 101 is shown with aphotoresist mask PR formed thereover. As with FIG. 1A, there are twoopen windows W through photoresist mask PR down to the top surface ofthe mask plate 101. The mask plate 101 may comprise a transparent,virgin, planar quartz plate with no layer of chrome formed thereon. Thetop surface of the mask plate 101 is flat or planar.

FIG. 9B shows the reticle 100 of FIG. 9A after a pair of initial featurerecesses 102 having sidewalls 102S and bottom surfaces 102B were etchedinto the top surface of the mask plate 101 in accordance with step B inFIG. 10A. In step B, the reticle mask plate 101 is etched with aconventional etching process as described above in step 13 of FIG. 2,exposing the bottom surfaces 102B of the recesses 102.

FIG. 9C shows reticle 100 of FIG. 9B after stripping the photoresistmask PR from the top surface of the mask plate 101 according to step Cin FIG. 10A.

FIG. 9D shows reticle 100 of FIG. 9C after deposition according to stepM in FIG. 10A of a conformal, sacrificial film 103C on top of thereticle 300 and the sidewalls and the bottom surface of the etchedinitial feature recess 102 leaving a narrower feature recess 102′representing a initial portion of a feature (feature 105F in FIGS.9F-9I).

FIG. 9E shows the reticle 100 of FIG. 9D after performing an anisotropicinside spacer etching process in accordance with step N in FIG. 10Aremoving the horizontally extending regions of the sacrificial film 103Cexposing the top surface of the mask plate 101 and the bottom surfaces102B leaving a pair of narrowed, and deeper features 102″ and leavingthe sacrificial film sidewall spacers 103S on the sidewalls 102S.

FIG. 9F shows the patterned reticle 100 of FIG. 9E after forming aconformal, actinic/light blocking, opaque-absorber film 105C thereoverin accordance with step P in FIG. 10B. The conformal, opaque-absorberfilm 105C covers the top surfaces of the reticle mask plate 101, thebottom surfaces 102B of both feature recesses 102″ and the exposedsurfaces of the sacrificial film sidewall spacers 103S. At this point,the opaque-absorber film 105C and sidewall spacers 103S have beendeposited within the recesses 102. The opaque-absorber film 105C isdeposited over the patterned reticle 100 with a relatively uniformthickness. As a result, the opaque-absorber film 105C produces an evennarrower feature recesses 102′″ defining preliminary features 105R. Theconformal, opaque-absorber film 105C preferably comprises an opaquematerial selected to have optical characteristics adapted to block theradiation (e.g. light) which can be employed for exposure (ontoworkpieces being manufactured) of patterns of damascene features to beformed in the mask plate 101. Two such damascene features 105F are shownafter completion of processing thereof as shown by FIGS. 9H and 9I.

FIG. 9G shows the reticle 100 of FIG. 9F after planarization of theopaque-absorber film 105C in accordance with step Q in FIG. 10B. Theplanarization step polishes away the conformal, opaque-absorber, actinicor light blocking film 105C from the top surface of the mask plate 101forming a pair of features 105F from the planarized portion of theopaque-absorber film 105C, inside the sacrificial sidewall spacers 103S.The sacrificial sidewall spacers 103S remain lining the initial featurerecess 102 with light blocking features 105F nested therein. However, atthis point the now unwanted sacrificial sidewall spacers 103S alsoremain in the feature recess 102, and the narrower feature recesses102′″ remain slightly shallower defining modified preliminary features105F.

FIG. 9H shows the reticle 100 of FIG. 9G after stripping the sacrificialsidewall spacers 103S from the recess sidewalls 102S (in accordance withstep R in FIG. 10B) leaving open spaces 107O between the planarizedconformal, opaque-absorber, actinic or light blocking features 105F andthe sidewalls 102S. The narrower and shallower feature recesses 102′″remain with open spaces 107O juxtaposed therewith. Sacrificial films,which are well known in the industry, can be carbonaceous materials thatcan be removed by oxygen based processes such as oxygen plasma strippingor other means.

Using this embodiment will allow filling of open spaces 107O and thencapping the reticle 100 as shown in FIG. 9I wherein the open spaces 107Ohave been filled with a transparent, phase-error-correction filler 107F(in accordance with step S in FIG. 10B) which can be solid or fluid(liquid or gas) to allow the exposure ambient to correct for any phaseerrors. This can be done for both via structures as well as line/spacepatterns. The index of refraction of the material in the open spaces107O/107F will determine the exact phase change in conjunction with thedepth of the trench 102. This embodiment allows precise control of thephase change of the actinic wavelength in the path through the spacearea by virtue of keeping the n*length constant, independent ofprocessing variables.

FIG. 9I shows reticle 100 of FIG. 9H after formation of protectivecapping layer 109 (in accordance with step T in FIG. 10B) over thesurface of device 100 leaving the open spaces 107O juxtaposed with theplanarized conformal, opaque-absorber, actinic or light blocking film105P. The capping layer 109 can be laminated, sputtered, or applied byany other method that does not interfere with the gap. Alternatively,the protective capping layer 109 can be deposited without filling thegap 107O. This is done by utilizing the dimensions of the gap. It iswell known in the industry that deposition non-conformally by means ofvapor deposition results in what is referred to as “poor gap fill” inthe industry. It is this very same “poor gap fill” that is employed atthis stage in the process to create an embedded/protected unfilled gapin accordance with this invention. At this point planarization (notshown) can be performed.

Ninth Embodiment: Open Peripheral Space Via Feature

FIG. 11 is a top perspective view depicting a reticle 110 in accordancewith this invention in which an annular, via type via feature 116F isformed for a structure, e.g. a semiconductor via, in a mask plate 111comprising a transparent reticle mask plate. The reticle 110 is made inaccordance with the method of this invention, as shown by the flow chartin FIGS. 10A/10B. As in FIGS. 9B and 9C and steps B and C in FIGS.10A/10B, first step is to etch the cylindrical initial feature recess112 down into the mask plate 111. Then line the cylindrical initialfeature recess 112 with a sacrificial layer (not shown) as describedabove (FIGS. 9E and 9F, steps M/N in FIG. 10A) and form a narrowercylindrical recess 112′. Next, line the narrower cylindrical recess 112′with an actinic absorber film as in FIGS. 9E and 9F (according to stepsP and Q in FIG. 10B) and planarize to form the actinic absorber film115P thereby producing a via patterning feature 116F. Then remove thesacrificial layer as in FIG. 9H and step R in FIG. 10B. A hollow well112W remains inside the conformal light blocking film 115P and there isan open, i.e. hollow, annular space 117O separating the planarizedconformal, opaque-absorber, actinic or light blocking film 115P from theside-walls of the original recess 112.

Tenth Embodiment: Open Peripheral Space Line Feature

FIG. 12 shows a top perspective view depicting a reticle 120 inaccordance with this invention in which an rectangular type linepatterning feature 126F is shown in a mask plate 121 (comprising atransparent reticle mask plate) with the planarized light blocking 125Pmaterial formed in a linear feature recess 122 leaving a narrow featurerecess 122W inside the light blocking film 125P. The reticle 120 is madein accordance with the method of this invention, as shown by the flowchart of FIGS. 10A/10B. In this case the first step is to etch arectangular initial feature recess 122 into the mask plate 121. Thenline the rectangular initial feature recess 122 with a sacrificial film(not shown) forming a narrower, rectangular recess 122′. Then planarizethe sacrificial, film to form a sacrificial sidewall spacer, asdescribed above with respect to FIGS. 9D-9E. Next line the additionalnarrower rectangular recess 122′ with a conformal light blocking filmcovering the sidewalls and bottom of the additional narrower rectangularrecess. Then planarize to produce a line patterning feature 126F. Ahollow well 122W remains inside the conformal light blocking film 125P.Then remove the sacrificial material leaving a peripheral open space127O surrounding the light blocking film 125P. In summary, the linepatterning feature 126F was formed in the rectangular initial featurerecess 122.

Damascene Reticle Chemical Mechanical Planarization

The processing required to achieve the above embodiments requires amethod of Damascene Reticle Chemical Mechanical Planarization (DRCMP) ofdamascene reticles which is different from Semiconductor Wafer CMP(SWCMP) of semiconductor wafers. The DRCMP method is different fromSWCMP because a reticle mask has a very different size and shapecompared to a silicon wafer. Also, the necessary films on a reticle maskcan be deposited in a different order from the order employed forperforming SWCMP on surfaces of a silicon wafer. The following exampleis provided to facilitate explanation of the process involved, while itis intended to be clear that the materials can be changed and/or theorder changed as will be well understood by those skilled in the art.

After a feature is etched into a reticle mask plate a conformal layer ofoptically transparent or light wave passing material is deposited. Thematerial can be selected from a range of materials that include but arenot limited to silicon dioxide (SiO₂), silicon nitride (Si₃N₄), andTEOS. Experimentation was done with silicon nitride. A problem with thestructure of this invention, is that a silicon nitride layer formed on asilicon, dioxide substrate is formed in the reverse order from thatusually employed by SWCMP planarization. A silicon nitride layer isusually used as a polish stop especially when polishing silicon oxide,as is well known in the industry. A number of silica based slurriesappropriate for such CMP processing are commercially available for theconventional SWCMP application. The relative polish rates, orselectivity, of these slurries typically range from about 3:1 to about4:1, with silicon dioxide having the higher polish rate.

In contrast in the case of the present invention, for reticle polishing,it is necessary to polish the silicon nitride and then to stop on thetop surface of the reticle which is composed of quartz that is amaterial which is very similar to silicon dioxide used in thesemiconductor industry. This requires provision of a slurry and aprocess with the reverse selectivity to the silica based slurriesdescribed above whereby the silicon nitride polish rate is substantiallyhigher than the silicon dioxide polish rate.

Slurry Formulation

A slurry formulation in accordance with this invention (described below)provides the needed “reverse selectivity,” with a ratio of polish rateswhere the silicon nitride is polished at a rate 3 to 4 times faster thanthe silicon oxide. Thereafter Tantalum Nitride (TaN) and Tantalum (Ta)were deposited to allow this material to be the internally placed lightblocking material. It was therefore necessary to employ semiconductorpolishing chemistries and processing to provide adequate removal of thematerials from the upper surface of the reticle mask plate withoutdisrupting the internally placed materials (with reference to the plate)and avoiding damage to the upper surface that would result in unwantedimaging on the reticle mask plate the image is projected upon.

Two exemplary slurry chemistries, tool types, and process parameters aredescribed next. There are many different process tools available and theprocess parameters will vary as the tool models vary as will be wellunderstood by those skilled in the art.

1) Ta CMP Slurry and Process, Stopping on Silicon Nitride

A semiconductor slurry is employed to remove TaN/Ta (TantalumNitride/Tantalum) stopping on the silicon nitride. The slurryformulation suppresses a silicon oxide and silicon nitride polish ratewhile maintaining a Ta polishing rate. A representative slurryformulation is shown in FIG. 15.

Damascene Reticle CMP Process

In FIG. 16, a table is shown with the processing parameters andequipment employed for performing an exemplary DRCMP process inaccordance with this invention.

2) CMP Slurry and Process for Removing Si₃N₄ and Stopping on SiO₂.

A slurry formulation is provided to remove silicon nitride and stop onsilicon oxide. The selectivities are reversed as compared to a normalsilica slurry. The slurry is prepared using a commercially availablefumed silica suspension in water. This starting material, as obtained,is stabilized in alkaline media, with potassium hydroxide or ammoniumhydroxide, to a pH of 9.5 to 12. The “reverse selectivity” slurry isprepared by adjusting the pH of the starting material to 2.4 (range 2.3to 2.5) with dilute phosphoric acid. This acid solution is prepared bydiluting 1 part of 86 percent phosphoric acid with 9 parts of water. Thefinal pH of the slurry is critical to achieving the desired ratio ofpolish rates. The preparation of this slurry is shown in the table ofFIG. 16.

CMP Process

In FIG. 17 another table is shown with an implementation, of the DRCMPprocess of this invention.

Reticle Polishing Carrier

FIGS. 13A and 13B show sectional and bottom views respectively of areticle polishing carrier 200 in accordance with this invention which isadapted for use with a wafer polishing tool for the purpose of reticlepolishing. FIGS. 14A and 14B show sectional and bottom viewsrespectively of the reticle polishing carrier 200 of FIGS. 13A and 13Bwith a reticle 210 inserted therein for polishing.

Referring to FIGS. 13A and 13B and 14A and 14B, a reticle polishingcarrier 200 in accordance with this invention is shown which is adaptedfor use with a wafer polishing tool (not shown) for the purpose of DRCMPreticle polishing. This is significant because such polishing tools aremade for SWCMP polishing of semiconductor wafers, which are round andhave a relatively small thickness on the order of only 0.03 inches(0.0762 cm) as compared to a damascene reticle that is square orrectangular that has a relatively large thickness of about 0.25 inches(0.635 cm,) which is approximately an order of magnitude larger.

Accordingly it was required to fabricate a reticle polishing carrier 200for a wafer polishing tool capable of accommodating a thick reticle 210shown in FIG. 14A. The reticle polishing carrier 200 is made ofcomponent parts that include a rigid base plate 201, a retaining ring205, and a reticle pad 207 to support the reticle 210 when it ispositioned in place, i.e. mounted, on the reticle carrier 200. The inneredges 206 match the external dimensions of the reticles to be process toretain such reticles 210 (shown in FIG. 14A/14B in position duringplanarization. The retaining ring 205 is made of a chemically inert yetdimensionally stable polymeric material such as PolyTetraFluoroEthylene(PTFE), Delrin, PolyEtherEtherKetone (PEEK), and other similarcommercially available materials.

The base plate 201 is preferably made of a rigid but corrosion resistantmaterial such as titanium or stainless steel. The base plate 201 and thereticle pad have a series of matching aligned passageways 208therethrough for exhaustion of air from the space between the base plate201 and the reticle 210. Additionally, a vacuum can be applied viapassageways 208 to retain the reticle 210 in place while the reticle isbeing transported into position for polishing on the CMP pad andtransported off the CMP pad after completion of polishing. During theactual polishing process air pressure can be applied to the back side ofthe reticle 210. This has the advantage of distributing the downwardlyapplied force across the entire area of the reticle 210, to improve theuniformity of material removal.

The thickness of a retaining ring 205 is selected to match the specifiedthickness of the reticle 210 so that the surface 210S of the reticle 210and the surface 205S of the retaining ring 205 are nearly coplanar. Thisis essential to enable the uniform removal of material from the squarereticle 210, using a semiconductor manufacturing tool designed for SWCMPprocessing of round wafers. By making the surfaces of the reticle 210and the retaining ring 205 nearly coplanar, the square shape of thereticle 210 will be properly embedded in the carrier 200, and a problemwill be avoided in that the straight edges of the reticle 210 will notbe disproportionately eroded by the polishing pad (not shown.) Thepolishing process can be further optimized for uniformity across thediameter of the reticle 210 by careful adjustment of the level of theexposed reticle surface 210S to be just above or just below (by plus orminus approx 0.010 inches) the surface 205S of the retaining ring 205.Raising the reticle 210 higher than the retaining ring 205 will increasepolishing at the edge of the reticle 210, while lowering the reticlesurface 210S will decrease polishing at the edge.

“Delrin is the brand name for an acetal resin engineering plasticinvented and sold by DuPont. Often marketed and used as a metalsubstitute, Delrin is a lightweight, low-friction, and wear-resistantplastic capable of operating in temperatures in excess of 90° C.″ Othernames for this compound include: PolyOxyMethylene (POM), acetal resin,polytrioxane and polyformaldehyde.”

Materials Suitable for a Blank Transparent Mask Plate

A list of materials preferred for blank transparent mask plates includescrystalline aluminum oxide, lithium indium selenide, fused silica. Othermaterials which may be suitable for various optical ranges. It isnecessary to match the material to the wavelength for either blocking orpassing the energy. For example aluminum oxide (Al₂O₃), and berylliumcan be used for x-ray. Calcium fluoride (CaF₂), zinc selenide (ZnSe),sodium chloride (NaCl), barium fluoride (BaF₂) can be used for infrared.Al₂O₃ which has several crystal forms which are called corundum,sapphire or ruby (depending on the color.) Sapphire comprises asingle-crystal form of Al₂O₃ can be employed for infrared opticalapplications. Sapphire is unique when compared to optical materialsuseful within its transmission range because it is strong, and tough.Also, sapphire is resistant to both thermal shock and chemicals, and canbe used at high temperatures. The thermal conductivity of sapphire isrelatively high despite its extreme electrical non-conductivity.Sapphire has a moderate refractive index, transparency in the visiblerange of wavelengths, good transmission and relatively low emission athigh temperatures plus unusual stability. CaF₂ can be used as a windowmaterial for both infrared and ultraviolet wavelengths. At wavelengthsas low as 157 nm, CaF₂ is useful for semiconductor manufacturing and asan ultraviolet optical material for integrated circuit lithography. CaF₂is transparent in the range from about 0.15 μm to about 9 μm at which itexhibits extremely weak birefringence. BaF₂ is transparent from theultraviolet to the infrared, from about 150-200 nm to about 11-11.5 μm,and can be used as a material to make optical components such as lenses.BaF₂ is used in windows for infrared spectroscopy and its transmittanceat 200 nm is relatively low at 0.60, but at 500 nm it goes up to0.96-0.97 and stays at that level until 9 μm, then falls off (e.g. 0.85for 10 μm and 0.42 for 12 μm). Magnesium fluoride (MgF₂) is transparentover a wide range of wavelengths. Windows, lenses, and prisms made ofMgF₂ can be used over the entire range of wavelengths from 0.140 μm(ultraviolet) to 8.0 μm (infrared).

ADVANTAGES OF THE INVENTION

The method of this invention increases the yield of optical projectionmask making in terms of resolution and the process window. The method ofthis invention improves yield in the fabrication of integrated circuitsdue to smaller line edge roughness. The method of this invention alsoimproves the lifetime of optical projection masks due to the fact thatthe patterns in the mask have damascene patterns embedded in a reticlemask plate.

The foregoing description discloses only exemplary embodiments of theinvention. Modifications of the above disclosed apparatus and methodswhich fall within the scope of the invention will be readily apparent tothose of ordinary skill in the art. While this invention is described interms of the above specific exemplary embodiment(s), those skilled inthe art will recognize that the invention can be practiced withmodifications within the spirit and scope of the appended claims, i.e.changes can be made in form and detail, without departing from thespirit and scope of the invention. Accordingly, while the presentinvention is disclosed in connection with exemplary embodiments thereof,it should be understood that changes can be made to provide otherembodiments which may fall within the spirit and scope of the inventionand all such changes come within the purview of the present inventionand the invention encompasses the subject matter defined by thefollowing claims.

1. A damascene method for manufacturing optical projection maskscomprising: patterning a substrate for an optical projection mask havinga first level of transmissivity with a feature recess; and filling saidrecess with a material having a different level of transmissivity. 2.The method of claim 1 including: said substrate comprising a transparentprojection reticle substrate having a top surface; forming said featurerecess in said top surface of said transparent projection reticlesubstrate; and forming a radiation transmissivity modifying material insaid feature recess.
 3. The method of claim 2 wherein said radiationtransmissivity modifying material comprises a material selected from thegroup consisting of an opaque material and a partially transmissivematerial.
 4. The method of claim 2 wherein a plurality of laminatedfilms are included in said feature recess with said laminated filmshaving different degrees of transmissivity.
 5. The method of claim 2wherein said radiation transmissivity modifying material is selectedfrom the group comprising: at least two deposited films including anopaque film and a transmissive film and an opaque film deposited with apartially transmissive material.
 6. The method of claim 2 including:forming a liner juxtaposed with said radiation transmissivity modifyingmaterial as a lens for focusing exposure rays at an edge of a pattern toincrease signal to noise levels; whereby scattering from a projectedpattern is minimized.
 7. The method of claim 2 including: forming asacrificial material in said recess; forming said radiationtransmissivity modifying material juxtaposed with said sacrificialmaterial; and removing said sacrificial material from said recess. 8.The method of claim 2 including: depositing said radiationtransmissivity modifying material as a film upon said transparentsubstrate; and planarizing said radiation transmissivity modifyingmaterial with a polishing slurry consisting of fumed silica, a pH offrom about 2.2 to about 2.6, and a 1:10 dilution in water on the orderof one part of about 84% to about 88% parts phosphoric acid to about 9parts water.
 9. A projection reticle formed in a transparent substratehaving a top surface comprising: a feature recess formed in said topsurface of said transparent substrate; and a radiation transmissivitymodifying material formed in said feature recess.
 10. The projectionreticle of claim 9 wherein said radiation transmissivity modifyingmaterial comprises a material selected from the group consisting of anopaque material, and a partially transmissive material.
 11. Theprojection reticle of claim 9 wherein a plurality of deposited films areincluded in said feature recess with said deposited films havingdifferent degrees of transmissivity.
 12. The projection reticle of claim9 wherein said radiation transmissivity modifying material is selectedfrom the group comprising: at least two deposited films including anopaque film and a transmissive film; and an opaque film deposited with apartially transmissive material.
 13. The projection reticle of claim 9wherein said radiation transmissivity modifying material comprises anopaque film juxtaposed with a phase error correction material selectedfrom the group consisting of a solid or a gas.
 14. The projectionreticle of claim 9 including: said recess having sidewalls; saidradiation transmissivity modifying material being spaced away from saidsidewalls by said phase error correction material.
 15. The projectionreticle of claim 9 including: a liner juxtaposed with said radiationtransmissivity modifying material as a lens for focusing the exposurerays at the edge of the pattern to increase signal to noise levels;whereby scattering from the projected pattern is minimized.
 16. A slurryfor reticle polishing comprising: fumed silica; a pH of from about 2.2to about 2.6; and a 1:10 dilution in water of 84-88% phosphoric acid.17. The method of claim 1 including a reticle carrier for a polishingtool capable of accommodating a reticle said reticle carrier comprisinga rigid base plate, a retaining ring, a reticle pad adapted forsupporting a reticle inserted onto said reticle carrier; and said baseplate and the reticle pad having a plurality of aligned passagewaystherethrough for exhaustion of air from, the space between said baseplate and a reticle; whereby generation of a vacuum can retain a reticlein place under vacuum conditions and application of air under pressurecan eject a reticle from said reticle carrier.
 18. The reticle carrierof claim 17 including a metal base plate that having a plurality ofpassageways therethrough.
 19. The reticle carrier of claim 18 includinga reticle pad installed on said metal base plate with matching alignedplurality of passageways therethrough.
 20. The reticle carrier of claim18 including a reticle holding ring made of a low friction material thatattachable to said base plate.